1. Field of the Invention
The present invention relates to a dielectric composition and a multi-layer ceramic capacitor embedded low temperature co-fired ceramic substrate using the same, and more particularly, to a dielectric composition and a multi-layer ceramic capacitor embedded low temperature co-fired ceramic substrate using the same, which is sinterable at a low temperature while showing a high dielectric constant.
2. Description of the Related Art
Recently, a technology of reducing a total volume of a product and increasing the degree of integration of a substrate not by mounting a device such as a surface mount device on the surface of the substrate but by embedding the device into a substrate having a circuit pattern is receiving attention according to the miniaturization and high frequency tendency of various electrical products.
When a chip-typed device on the substrate is replaced with a layer-typed device (e.g., a capacitor), an increase of the volume caused by the chip may be suppressed. Also, the layer-typed capacitor has more excellent high-frequency property (e.g., smaller parasitic inductance) than the chip-typed capacitor. Accordingly, various attempts have been made to embed the chip into the substrate.
A Printed Circuit Board (PCB) is generally divided into two types according to materials forming a dielectric layer. One PCB applied with a polymeric organic material as a dielectric layer is more widely used. A plating method is used to form a circuit pattern on the PCB. On the other hand, a screen printing is mainly used to form the circuit pattern on the other PCB, the dielectric layer of which is formed of a ceramic material. In this case, the PCB is manufactured by sintering the dielectric layer and an electrode simultaneously. The sintering process is generally performed at a temperature of about 800° C. or more.
Two types of substrates have very different properties in the aspects of a material and a manufacturing process. However, their structures are very similar to each other in that the circuit pattern is formed in a laminated body of multilayer. Accordingly, their applicable ranges overlap each other in many cases. There are few technologies to which both types of substrates may be together applied because the material and the manufacturing process of each type is entirely different from each other as described above.
In a case where the capacitor is embedded into the ceramic substrate, a dielectric layer for a capacitor and an internal electrode are formed and simultaneously sintered between ceramic green sheets including a ceramic and a glass. In case of the capacitor, the dielectric constant property is important. BaTiO3 may be used as a main component of composition used in the dielectric layer instead of Pb because of a high dielectric constant and environmental reason. However, BaTiO3 may be sintered at a temperature of about 1400° C. or more unless a sintering additive is used. Moreover, although the sintering additive is used, BaTiO3 is difficult to be sintered at a temperature of about 1000° C. or less.
In a ceramic substrate embedded with the capacitor, the dielectric constant and the sinterable temperature are important. In case of the ceramic substrate, an electrode is formed by printing a metal such as Ag or Cu, which is sintered to form a circuit pattern on the substrate. Accordingly, the firing temperature of the ceramic substrate must be lower than at least the melting points of Ag and Cu. However, when the capacitor is embedded, the firing temperature of the capacitor must be lower than at least the melting points of Ag and Cu because the embedded capacitor must be together sintered. In this case, as described above, the dielectric layer may not be completely sintered. Moreover, the dielectric constant may be reduced.
Accordingly, the development of a technology capable of manufacturing a low temperature co-fired ceramic substrate embedded with a multi-layer ceramic capacitor showing a high dielectric constant after even a low temperature firing is required.